From the Encyclopaedia Judaica 10:988
The first biblical reference to the “brook” Kidron occurs in connection with Davids ABsalm (II Sam. 15:23) In the time of divided monarchy, the reforming Kings of Judah, Asa, Hezekiah, and Josiah, cast away and burnt the various idols which defiled Jerusalem there (I Kings 15:13 ; II Kings 23:4, 6,12 ; Chron. 15:16 ; 29:16) Jeremiah included the Kidron within the area holy to the Lord (31:39-40)
In later times the central parts of the valley was called the valley of Jehoshaphat and was assumed to be the place the dead were resurrected. In this legend, as adapted by Muslims, all menn had to cross the valley on a sword suspended over it.